1. Field of the Invention
The present disclosure relates to control of a document reading apparatus including a member for cleaning a platen glass.
2. Description of the Related Art
In sheet through-type automatic document reading apparatuses, an image on the document surface of a document conveyed by conveyance means is read by stationary image reading means. Those apparatuses are advantageous in that they can be reduced in size and in cost and noise and have high productivity when compared with platen set-type apparatuses which read a document at a stop by moving image reading means.
In the case of the sheet through-type apparatuses, the image reading means requires a structure fixed at a particular position and adjusts a focus on a document surface through a platen glass. In the sheet through-type apparatuses, therefore, the quality of the read image is easily influenced by foreign matters such as paper dust and dirt which obstruct the reading position. This is because, for example, a streak-like image noise (hereinafter referred to as “streak noise”) occurs at a portion of the read image that corresponds where light is blocked by foreign matters such as paper dust or dirt left on the document reading surface such as a platen glass.
When a document having information recorded thereon is conveyed in the document reading apparatuses, the conveyance of paper inevitably causes paper dust to adhere on the reading surface. In this respect, the document reading apparatuses require means for removing foreign matters such as paper dust on the document reading surface. In situations where an excessive amount of paper dust is produced, the document reading apparatuses further require means for preventing streak noise.
In view of the foregoing situations, a variety of document reading apparatuses having a member for cleaning a paper conveyance path have been proposed. For example, Japanese Laid-Open Patent Publication No. 2005-204007 discloses a document reading apparatus having a cleaning member. The cleaning member is provided at a platen roller. The document reading apparatus changes the state of the cleaning member between a state in which it abuts on a platen glass and a state in which it does not abut on the platen glass. The document reading apparatus brings the cleaning member into abutment with the platen glass in a period during which no document is conveyed (for example, a period immediately before document conveyance operation and a period immediately after the end of conveyance operation). The platen glass surface is thus cleaned in the period during which no document is conveyed.
Japanese Laid-Open Patent Publication No. 04-153140 discloses a paper conveyance apparatus having cleaning means. The cleaning means includes a shaft provided at a position opposed to an optical system. The shaft has a brush attached thereto. The paper conveyance apparatus periodically rotates the shaft thereby carrying out periodical cleaning for removing paper dust accumulated in a conveyance path.
The apparatuses in the related art as described above perform cleaning such that the cleaning member or the brush abuts on the platen glass between document sheets passing through on the platen glass. The cleaning member thus comes into abutment with the platen glass in the absence of document paper on the platen glass. As a result, after cleaning, paper dust may be left on the platen glass upstream in the conveyance direction from the point where the conveyed document starts coming into contact with the platen glass. When a document is newly conveyed in a state in which paper dust left upstream underlies the document, streak noise as described above may occur in an image of the document.